Iowa City, IA—Over the last 20 years, the prevalence of attention-deficit/hyperactivity disorder (ADHD) has burgeoned in U.S. children and adolescents, and the dramatic increases occurred despite sex, race/ethnicity, family income, or geographic area.

A new study in JAMA Network Open reports that ADHD has increased in estimated prevalence among U.S. children and adolescents from 6.1% to 10.2% between 1997 and 2016.

University of Iowa–led researchers admit, however, that they are still not sure why.

Their observational study involved 186,457 U.S. children and adolescents, ages 4 to 17 years, with data collected from 1997 to 2016 as part of the National Health Interview Survey. All participants had been diagnosed with ADHD by a physician or other healthcare professional

Results indicated that age, sex, race/ethnicity, family income and geographic region individually influenced ADHD diagnoses, although all these subgroups showed an increase in prevalence from 1997 to 2016.

“Nonetiologic factors may partly explain the apparent increase in the prevalence of diagnosed ADHD in this study,” the study authors state. “Over the past 20 years, there have been expanded continuing medical education efforts about ADHD that enhanced physicians’ sensitivity to the diagnosis of ADHD.”

The study also discusses changes in diagnostic criteria, which could have contributed to the increased number of children being diagnosed with ADHD. The authors also noted that “increased public awareness, improved access to health services, and improved referral from primary care and communities to specialty mental health services may increase the likelihood of ADHD being identified on screening and diagnosis.”

Specifically, researchers suggested that increased rates of diagnosed ADHD among black and Hispanic youths could indicate increased access to care and decreased stigma in those communities for receiving an ADHD diagnosis.

Results of the study indicate that prevalence of ADHD was 14.0% (95% CI, 13.1%-15.0%) in boys and 6.3% (95% CI, 5.6%-7.0%) in girls. Race and ethnicity also appeared to play a role, the study indicates, finding rates of 6.1% (95% CI, 5.2%-7.0%) in Hispanic youth, 12.0% (95% CI, 11.1%-12.9%) in non-Hispanic white youth, and 12.8% (95% CI, 11.0%-14.5%) in non-Hispanic black youth.

Another possible explanation for the across-the-board increases in diagnoses is that ADHD has a genetic component, with an estimated heritability of 70% to 80%, researchers posited, noting that environmental risk factors are also believed to contribute to the development of ADHD. “Prenatal and perinatal risk factors, including preterm birth, low birth weight, maternal cigarette smoking, and maternal use of certain medications or illicit substances during pregnancy, have been associated with ADHD risk,” they write.

The study does not suggest that ADHD is overdiagnosed, however, pointing out that the “perception was not supported by scientific evidence based on review of prevalence studies and research on the diagnostic process.”

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